Thursday, 5 November 2009

The Queen Elizabeth Class Aircraft Carriers

The aircraft carrier is the last true capital ship of any navy's surface fleet.

While most of a navy's ships are primarily of use in war at sea,the aircraft carrier is equally powerful in air wars and land wars.

Although the aircraft carrier is the most expensive ship in any surface fleet,it is also the vessel which is most useful most often,and hence most resource effective.

While other ships may have a limited ability to attack land targets,the aircraft carrier can also find targets on land and conduct a sustained land attack campaign.

While other ships may have a limited ability to engage aircraft,in an air battle the aircraft carrier is limited only by the airgroup it can carry.

While other ships may have a limited ability to engage surface ships and submarines,the aircraft carrier can detect and engage those targets from hundreds of miles away.

In addition to it's more common air attack role,the aircraft carrier has been used extensively,especially by the Royal Navy,in the air assault role.

Indeed,the aircraft carrier in it's air assault or "Commando carrier" role is the only ship which can conduct an amphibious assault without exposing it's self to land based threats.

The aircraft carrier's large internal volume allows it to carry extensive medical facilities,it is the ideal "primary casualty reception ship",particularly during air assault operations.

The flexible nature of a large aircraft carrier allows it to economically replace a larger number of smaller,single role ships.

Most importantly,the large aircraft carrier is the most cost effective means of deploying expeditionary air power.

The cost savings inherent in using carrier aviation can exceed the cost of buying and operating an aircraft carrier by a factor of ten.

Whilst the aircraft carrier is essential to naval operations,it is these cost savings which make carrier aviation essential to air and land warfare.

A small number of large multirole air attack/air assault ships provides a highly capable and flexible core to a surface fleet.

For the British Royal Navy,four purpose designed large multirole aircraft carriers could replace Her Majesty's Ships:Invincible,Illustrious,Ark Royal,Ocean,Albion,Bulwark and the Royal Fleet Auxiliary Argus.

Such a fleet would result in a robust and cost effective ability to conduct the whole spectrum of combat operations.

However,instead of designing a large multirole aircraft carrier the Royal Navy is currently procuring the much smaller Queen Elizabeth class.

While the Queen Elizabeth class has a secondary role as a "Commando carrier" it does not have sufficient capacity to replace the Royal Navy's three current assault ships.

Equally,the small air wing of the Queen Elizabeth class limits the cost savings which it can achieve in the application of expeditionary air power.

The current plan to purchase the vertical landing F35B for the Royal Navy's carrier wing will result in an air wing which is very limited in capability.

The F35B is less capable than the cheaper conventional landing F35C.

Fixed wing Airborne Early Warning (A.E.W.) and other support aircraft cannot operate from the Queen Elizabeth class aircraft carriers unless the ships are configured for catapult operation.

The rotary wing alternatives are much less capable and are not able to support air combat operations far from the carrier.

This lack of fixed wing capability creates a dependence on expensive land based support aircraft and bases.

The current plan to build the Queen Elizabeth class as vertical landing carriers will result in higher overall costs,greater risk and lower return on investment.

The Queen Elizabeth class aircraft carriers also suffer from a number of deficiencies in their design.

Many of the negative features of the Queen Elizabeth class appear to be taken directly from the troubled French aircraft carrier Charles de Gaulle.

Both ships are too slow,too small and have inefficient deck layouts.

The flight deck layout of the two ships is identical apart from the second island on the conventionally powered Queen Elizabeth class.

Problems inherent in the deck layout of the Queen Elizabeth class aircraft carrier when configured for catapults and arrestor wires are as follows:

The utility of flight deck areas adjacent to the aft island is degraded by their small size,awkward shape and proximity to the superstructure.

The turbulent wake from the aft island affects both deck operations and flying operations as aircraft must pass behind the island as they approach to land on the carrier.

Corrosive exhaust gasses from the aft uptake also have negative effects on both deck and flying operations.

4.The port catapult cannot be used without interfering with the operation of both the landing area and the starboard catapult.

5.The proximity of the aft aircraft lift to the arrestor wires and landing area precludes aircraft movements from the starboard aftermost parking area,"Fly 3", when the aft lift is being used during landing operations.

6.The port aftermost parking area,"Fly 4",has very low utility/low value as during landing operations it is isolated from the aircraft lifts and other aircraft arming,fuelling and handling areas whilst the catapult it services cannot be used or prepared for use.

Note the way the landing area cuts the flightdeck in two on the French aircraft carrier Charles de Gaulle.

Solutions to these problems shown on the "Improved Queen Elizabeth class" are as follows:

A.Mounting the starboard catapult along the deck edge allows the catapult to be used or prepared for use without interfering with the operation of either the landing area or the port catapult.

This also minimises the deck area swept by aircraft launching from the catapult and hence increases the parking space available in the forward,"Fly 1",parking area during single catapult operations whilst permitting unrestricted access to the main aircraft arming,fuelling and handling areas and aircraft lifts.

B.Mounting the port catapult forward,parallel to the starboard catapult and the landing area and with adequate separation from them,allows it to be used or prepared for use without interfering with the operation of either the landing area or the starboard catapult.

This large and regularly shaped,"Fly 1",parking area supports the starboard catapult during single catapult operations whilst also having unrestricted access to the main aircraft arming,fuelling and handling areas and aircraft lifts.

With both catapults and the landing area in parallel,all can be pointing into the wind at the same time.

Mounting both catapults alongside eachother on the fore deck allows this deck to be inclined up towards the bows.

This increases the safety and performance of the catapults whilst also permitting aircraft launches when the ship is pitching heavily.

In addition,the resulting higher bows will help to keep the deck dry in heavy weather.

The angle of incline of the foredeck must be sufficiently modest to permit this area to be used for aircraft parking.

C.The main aircraft arming,fuelling and handling area,"Fly 2",is large and unobstructed with unrestricted access to both catapults,both aircraft lifts and the landing area.

The future American aircraft carrier CVN 78 uses this layout.

D.The small and awkwardly shaped forward part of the port aft parking area,"Fly 4",can be used as a parking area for flightdeck tractors,cranes,fire tenders and other equipment which does not need to regularly cross the landing area.

E.Locating the island to port,aft of the landing area in "Fly 4",utilises low utility/low value deck space and hence frees up high utility/high value deckspace elsewhere.

A small narrow island takes up less deckspace and creates less air turbulence in it's wake.

Aircraft approaching to land from starboard do not have to fly through the turbulent wake and corrosive exhaust of an island on the port side whilst locating the island well aft also reduces the effects of turbulence and exhaust gasses on deck operations.

F.Moving the aft aircraft elevator further aft reduces the size of the isolated,limited utility "Fly 3" parking area whilst increasing the size of the high utility/high value "Fly 2" aircraft arming,fuelling and handling area.

G.The now smaller and still isolated,low utility/low value "Fly 4" area aft of the island allows helicopter operations to take place without interfering with fixed wing flying operations.

This area can also be used to park aircraft and equipment which would not routinely need to cross the landing area.

Carrying their heavy,armoured strength deck at hangar deck level,American aircraft carriers traditionally had narrow hangar decks but wide lightly built flight decks supported by sponsons,modern American carriers continue this trend even with their strength deck now at flight deck level.

With their heavy,armoured strength deck at flightdeck level,British carriers had narrower flight decks but hulls which flared out above the waterline to give a wide hangar deck.

The French aircraft carrier Charles de Gaulle has an American style narrow,vertical hull with wide sponsons.

With no armoured decks,the Queen Elizabeth class could have had the advantages of both designs but instead they have an American style narrow hangar deck just like Charles de Gaulle.

The new Italian aircraft carrier Cavour has a British style flared hull,giving greater hull volume at the hanger deck level.

To mitigate this risk it is necessary to ensure a high degree of separation between the two engines.

On the Queen Elizabeth class the engines are located fore and aft of the forward aircraft elevator on the starboard side.

This in turn results in the need for each engine to have it's own seperate uptake for exhaust gasses as the position of the aircraft elevator precludes ducting both engines to a single uptake.

Such an arrangement takes up a substantial area of high utility/high value deck space and reduces the utility of nearby open deck space whilst also afflicting flying and deck operations with the effects of air turbulence and exhaust gasses in the wake of the islands.

The designers of the Queen Elizabeth class claim to have made a virtue of this necessity by constructing two islands around these two uptakes.

However the advantage of having two islands is questionable at best.

Relocating the engines to the port side,allows an exhaust duct to be run below the outer edge of the flight deck,connecting multiple engines to a single uptake.

This arrangement takes up little usable volume.

Engines can intake air locally and laterally,it is only the exhaust gasses which need to go through the uptake duct.

Two of the biggest problems with the Queen Elizabeth class are the low speed and small size of these ships.

Ship speed is a critical factor in aircraft carrier operations as it allows the ship to generate "wind over deck",this being the sum of wind speed and ship speed.

As fixed wing aircraft must land and take off at a particular air speed,the relative speed between the aircraft and the ship is equal to airspeed minus speed of the "wind over deck".

Thus the higher the speed of the ship,the lower the relative speed between the ship and the aircraft on landing and takeoff.

Reducing this relative speed has two advantages.

Firstly it makes take offs and landings easier for the pilot as things happen more slowly.

Secondly it reduces the amount of energy which must be transferred from the aircraft on landing or given to the aircraft on takeoff.

As kinetic energy is proportional to the square of velocity,small reductions in relative speed result in large reductions in kinetic energy.

Reducing this energy transfer reduces demands on catapults,arrestor wires and airframes on a conventional aircraft carrier.

It is also very important in conducting flying operations by other means which do not involve catapults or arrestor wires.

Ship speed and flightdeck height are also critical safety factors in helicopter operations.

High ship speed also gives the aircraft carrier greater strategic mobility,allowing it to get to the operational area more quickly.

Tactically,speed is important with regards to the submarine threat.

Submerged conventional submarines have limited speed and endurance and can be outrun by most surface ships.

However,some nuclear powered boats are allegedly capable of very high speeds.

Some Russian submarines are credited with "quiet speeds" of 28 knots and maximum speeds of 35 knots.

An aircraft carrier which cannot match such speeds is vulnerable to being hunted by nuclear submarines.

Historically most aircraft carriers have made speeds in excess of 30 knots,with some making close to 35 knots.

As speed increases,so does the need for power to generate that speed and the need for fuel to generate power.

For a given size of ship,increased volume and weight dedicated to ship's fuel and power means less volume and weight for other things such as ammunition and aviation fuel.

Hence there are design incentives to restrain ship speed just as there are incentives to increase ship speed.

The question is at what speeds do these conflicts balance out?

Historically,most large aircraft carriers have been capable of speeds of 32-35 knots.

The Queen Elizabeth class are said to be capable of 25-28 knots.

These speeds are well below what is generally regarded as practical.

A longer hull is more hydrodynamic and requires less power to generate a given speed or generates a greater speed for a given power.

A longer ship also offers more deck space,internal volume and payload,all of which are of great benefit to aircraft carrier operations.

On a conventionally equipped ship,increasing flight deck length also increases the flightdeck width available for catapults ahead of the angled landing area.

Additional length is also of great benefit for ships which utilise rolling landings and/or rolling take offs.

A longer ship will pitch less in a given sea state.

As angle of pitch is a limiting factor on flying operations,so the longer ship will permit flying in worse weather conditions.

The modular nature of the Queen Elizabeth class makes it a simple matter to increase the ship's length by adding a hull plug at an early stage in the build.

A 30 metre hull plug would add enough space for a third gas turbine and the fuel it requires.

It would also increase hangar space sufficiently to accomodate 6 additional fighter aircraft while adding enough deck space for an additional 12 aircraft in the deck park.

With space for an airgroup of 58 aircraft the ship will be able to carry a full range of large support aircraft and a larger fighter wing.

The increase in hull length combined with the power of a third turbine will increase ship speed to around 30 knots.

It would be neccessary to make changes to the propulsion (screws,shafts and motors) to match the increased power output but again such changes are easily accommodated at this very early stage in the ship's build.

One of the main rasons for a nation to buy an aircraft carrier is it's cost effectiveness when compared to land based aviation.

Aircraft carriers are often located closer to areas of conflict than air bases.

This reduction in the distance between the aircraft's base and it's area of operation (and the great speed with which the sortie generating factory that is an aircraft carrier turns aircraft around between sorties) allows each aircraft to fly more sorties in a day.

If each aircraft flies more daily sorties then fewer aircraft are required.

Similarly,for more persistant sorties,shorter distances translate to longer time on station and hence fewer aircraft required to maintain round the clock coverage.

Carrier based aircraft also require less aerial refueling support.

In the major air wars which the United Kingdom has been involved in since 1945,carrier based aircraft have typically generated double the sortie rates of their land based counterparts.

For example,during the six week long air war over the Falkland Islands,carrier based fixed wing aircraft flew 1561 sorties while land based bombers completed just 5 tactical sorties.

Doubling the aircraft's sortie rate would halve the number of aircraft required to generate a given effect on the enemy.

Thus a carrier wing of 48 aircraft could do the same job as 96 land based aircraft.

However,this does not represent a saving of just 48 aircraft.

For every 4 aircraft with British Royal Air Force (R.A.F.) frontline squadrons there is typically 1 aircraft with an Operational Conversion Unit (O.C.U.) being used to train pilots on that aircraft type and a further 2 aircraft as attrition and maintenance reserves in what is known as the "depth fleet".

Fielding a wing of 48 frontline fighters then requires approximately 84 aircraft.

Thus if a carrier wing of 48 aircraft does the job of 96 land based aircraft we may reduce the size of our fighter aircraft fleet by 84 aircraft in total and still generate the same effect on target.

The operating costs of the Royal Navy's expected future carrier aircraft,the F35 Lightning II,are not known at present.

Clearly the annual savings generated by the aircraft carrier are immense.

It is noteworthy that the size of the airgroup dictates the size of this financial saving.

An air wing of just 36 fighters would typically generate the same workrate as 72 land based fighters.

This would allow us to cut the size of our air fleet by 36 frontline aircraft and 63 aircraft in total,again based on current ratios of frontline aircraft to training aircraft and the depth fleet.

At £11,000,000 per combat aircraft per year that equates to a saving of £693,000,000 a year for 63 fewer aircraft.

Which is £231,000,000 less than we could save with a 48 strong carrier airwing.

In other words the larger our aircraft carriers and the bigger their air wings the more money we save.

Also,whether an aircraft carrier has 40 aircraft aboard or 80,it still requires the same number of escorts to defend it and the same number of replenishment vessels to supply it.

But the ship with 60 aircraft may generate twice as many sorties as the ship with 30 aircraft.

Thus the cost per sortie "overhead" of the aircraft carrier and it's escorts is usually lower for the larger aircraft carrier than for the smaller ship.

The size of an aircraft carrier's airgroup then is a major factor dictating the efficiency with which the ship can generate sorties.

The greatest financial benefits come from the aircraft carrier with the largest practical air wing.

There are clearly significant financial savings to be had from increasing the size of the Queen Elizabeth class carriers so they can carry more aircraft.

The costs of buying aircraft carriers,let alone the cost of increasing their size,is inconsequential when compared to the massive cost savings they generate.

In summary,although the current Queen Elizabeth class aircraft carrier design suffers from a small airgroup,inefficient deck layout and slow speed,all of these problems can be easily rectified at an early stage in the build process.

With a 30 metre hull plug,a third gas turbine,a single island located to port and a revised deck layout with catapults and arrestor wires these ships will be more cost effective and more combat effective.

The cost of such modifications is repaid many times over by the additional savings which they permit.

your ideas are most intriguing however i must find a huge fault in one of them. an aircraft carrier simply cannot have the island located to the port side. the only type of carrier ever built that did not feature a starboard island was the akagi and hiryu classes built by japan in the second world war. no one seems to know why but the aircraft onboard suffered alarming loss rates upon landing with aircraft colliding with the bridge.

The idea of putting the island on the right-hand side originated when the royal navy was developing it first carriers. When the engine of a plane was running, the propellor rotated clockwise from the pilots point of view and thus caused a small bit of a tenacity in which aircraft would automatically pitch to the left upon take off. It was int he best interest of the Navy to avoid aircraft from hitting the bridge and other area's vital to the control of the ship and air movements and therefore, the island was placed on the right- hand side of the flightdeck.

I agree, the island on the left sucks. 90k£ an hour for Typhoon is totally dubious : a B-52 costs only 69k$/h, a F-22 68k$, a F-15 about 44k$, a F-18 about 24k$. Eurocanards have been created around much less thirsty engines and for low maintenance : Grippen costs are known to be around 5k$/hour and Rafale about 8k€/8k5€.9k£ and not 90k£ looks much more logical for Typhoons.Anyway, the QE class concept is fixed : No CATOBAR, they won't be real aircraft carriers and F-35 is very likely to melt the deck :) @280M$ each, well, poor brits, you'd better have listened to the frenchs : Rafale works wonderfully. Osprey will really sucks : they have a tremendous accident rate, they're the most costly military aircraft : 83k$/hour and @77M$ each, they're not a bargain... It'll be smth around 230M$/plane to make it replace Hawkeyes...But brits can always ask Dassault to take the Breguet 941S out of its drawer : I don't see any other transport aircraft being able to operate their carriers without catapults or tremendous high costs : 8 tons payload, takes off in 185m, lands in 120m... 1961 french technology...

These ships are designed and built in such a way that a 80 metre 250' hull block being added in the future would not be difficult. They would then have a better lenght to beam ratio and with added power and azmuith pod..... You can see where this and these carriers are going.

"an aircraft carrier simply cannot have the island located to the port side. the only type of carrier ever built that did not feature a starboard island was the akagi and hiryu classes built by japan in the second world war. no one seems to know why but the aircraft onboard suffered alarming loss rates upon landing with aircraft colliding with the bridge."

Are you really suggesting that naval pilots who are intensively trained fly their aircraft with great precision into the wires on an aircraft carrier's deck are going to get "confused" and fly into an island sixty feet to the left of their intended landing area?

Have you seen how close to those wires aircraft are parked on deck?

Do you understand that every day hundreds of pilots land their aircraft on aircraft carriers without hitting those parked aircraft?

one of our readers has said the following (http://futureadf.blogspot.co.uk/p/the-australian-aircraft-carrier.html):

"the bridge is on the starboard side, unlike in the G.L. linked article, because pilots aborting their landings tend to pull away to the left"

This is not correct.

Pilots aborting landings fly in a straight line along the axis of the landing area and therefore cannot hit an island on the port side.

Even if they attempted to do something as silly as losing altitude and speed by executing a hard left turn whilst bolting they simply could not turn hard enough to hit an island which is sixty feet to the left of the wires.

"These ships are designed and built in such a way that a 80 metre 250' hull block being added in the future would not be difficult. They would then have a better lenght to beam ratio and with added power and azmuith pod..... You can see where this and these carriers are going."

Length to beam ratios?

Azimuthing pods?

What a pleasure it is to read a comment by someone who actually knows what he is talking about.

Perhaps you could explain why,but before you do please read the responses to the above comments.

Anonymous said...

"90k£ an hour for Typhoon is totally dubious : a B-52 costs only 69k$/h, a F-22 68k$, a F-15 about 44k$, a F-18 about 24k$."

That "dubious" figure is officialy published by the British government,it is entirely correct.

Anonymous said...

"Eurocanards have been created around much less thirsty engines and for low maintenance : Grippen costs are known to be around 5k$/hour and Rafale about 8k€/8k5€.9k£ and not 90k£ looks much more logical for Typhoons."

Perhaps you should educate yourself about the difference between aircraft capital costs and marginal costs,you do not appear to understand the difference.

Anonymous said...

"It'll be smth around 230M$/plane to make it replace Hawkeyes..."

The cost of acquiring and operating Hawkeyes is a small fraction of the cost of upgrading and operating both the Sentry and Crowsnest systems.